Air filtration device having tuned air distribution system

ABSTRACT

A filtering device  10  that includes a housing  12  having a plurality of subsections  32, 34 , and  36  where each subsection is adapted to receive a filter element  26, 28 , and  30 . An inlet  18  is disposed at a first location on the housing  12 , and an upstream air distribution system is placed in fluid communication with the inlet  18  and with each of the subsections  32, 34 , and  36 . A downstream air distribution system is located in fluid communication with each subsection  32, 34 , and  36 , and an outlet  20  in fluid communication with the downstream air distribution system. The upstream and downstream air distribution systems are constructed to cause the same airflow velocity through each subsection. Using such a construction, overall product service life may be increased while minimizing pressure resistance of the total filter.

This invention was made with Government support under contract with theDepartment of Defense, Contract No. W911SR-09-C-0037. The Government hascertain rights in this invention.

The present invention pertains to a filtering device that has a housingthat includes a plurality of subsections where each subsection isadapted to receive a filter element. The housing has one or more airdistribution systems constructed to cause the same airflow velocitythrough each housing subsection.

BACKGROUND

Respirators that filter air for breathing are frequently worn byindividuals who work in areas where contaminated air is present. Therespirators may operate under negative pressure, in which the wearer'slungs provide the power that draws air through the filter (see, forexample, U.S. Pat. RE35,062 to Brostrom et al.), or they may operateusing positive pressure, in which a fan or other device drives theambient air through the filter (see, for example U.S. Pat. No. 7,748,381to Croll et al). A powered air purifying respirator (PAPR) is oftendesired by users because the wearer does not have to supply the energyneeded to force the ambient air through the air filter. The weareraccordingly feels more comfort and may use the saved energy for othertasks.

PAPRs typically have (i) an electric motor and blower unit to force theair through the filter, (ii) a facepiece for delivering the clean air tothe user, and (iii) a power source, such as a battery pack, to supplythe energy needed to power the device. Known PAPRs have been assembledin a variety of configurations, but two common types are belt pack PAPRsand helmet PAPRs. Belt pack PAPRs typically have the filtering unit wornabout the user's waist, whereas helmet PAPRs have the filtering unitcontained within the helmet. In both systems, an electrically-poweredfan drives or draws the air through the filter cartridges, through thehose, and into the facepiece interior. Because the fan does the workrequired for air movement through the PAPR system, the user is able tocomfortably receive a clean supply of air with little effort.

Helmet-style PAPRs typically use a supported filter bag to filter airbefore it enters the interior gas space for breathing. The filter bagholders sometimes have only limited or no support through the center ofthe filter bag because the airflow alone is sufficient to keep thefilter layers separated. FIG. 1 shows a filter support used in somehelmet-mounted respirators. The filter bag holder 110 is designed tosupport a flat filter bag in an arcuate form to fit within the crownspace of a helmet. The holder 110 is constructed of two members 112 and114, with the smaller member 114 being held in compression to provide anopening 116 between the two members at one end thereof. Both members 112and 114 include a plurality of openings 118 and 120, respectively, thatare aligned along the length of the holder 110. The filter bag holder110 is designed primarily to maintain the filter bag in an arcuateshape. An example of a helmet-mounted PAPRs system is disclosed in U.S.Pat. No. 4,280,491 to Berg et al.

Another product that maintains the filtering bag in an arcuate shape isdisclosed in U.S. Pat. No. 6,279,570 to Mittelstadt et al. As shown inFIG. 2, this filter support 200 has ribs 210 and 220 that are generallyaligned with the longitudinal axis of the device. Some of the supportribs 210 are laterally offset from adjacent ribs 220. FIG. 3 shows howthe filtration bag 310 may be placed around the support 200 in a helmet300.

Another PAPR is described in International Publication WO 2011/126884 toAusen. In this device, the blower is placed within the helmet along withthe filter media and a plenum that delivers ambient air to the filter.Air that exits the filter media then passes into another plenum where itis pulled into a blower assembly located centrally within the helmet.After passing through the blower assembly, the filtered air is thendelivered to the wearer via a filtered air outlet and a filtered airpassageway.

Although these conventional filtering devices have provided good supportfor the filtering material and have demonstrated good filtration of theair that passes through the device, the devices have not allowed for thecontrolled flow of air through the filter media. Without such controlledor controllable flow, certain portions of the filter media may becomeexpended before others, resulting in an earlier ending of the servicelife.

SUMMARY OF THE INVENTION

The present invention provides a new filter cartridge that comprises ahousing, an inlet, a first or upstream air distribution system, a secondor downstream air distribution system, and an outlet. The housingincludes a plurality of subsections, each subsection adapted orconstructed to contain a filter element. The inlet is disposed at afirst location on the housing. The upstream air distribution system isin fluid communication with the inlet and with each of the subsections.The downstream air distribution system is located in fluid communicationwith each subsection, and the outlet is in fluid communication with thedownstream air distribution system. The first and/or second airdistribution system(s) is or are constructed to cause the same airflowvelocity through each subsection.

The present invention is beneficial in that filter service life may beextended since each subsection receives the same airflow velocity. Eachfilter element may be exposed to similar volumes of airflow andcontaminants, causing no filter element to reach the end of its servicelife substantially before the others. Overall product service life maybe increased. The pressure resistance of the total filter also may beminimized because the air flow may pass through all of the filter mediaequally, thereby increasing the amount of filter media beingused—compared to a filter with air flow distribution issues where allair flow is pushed through a small portion of the available media.

GLOSSARY

The terms set forth below will have the meanings as defined:

“active particulate” means particles or granules that are speciallysuited to perform some action or function such as sorption (adsorptionand/or absorption), catalysis, and ion exchange;

“air distribution system” means a part or combination of parts whichassist in controlling air flow;

“air flow” means greater than insignificant or immeasurable airmovement;

“airflow velocity” means a pressure exhibited by moving air relative toa baseline pressure;

“baseline pressure” means pressure measured at ambient pressure or at alocation common to air flows to or from other locations where pressureis measured;

“clean air” means a volume of ambient air that has been filtered toremove contaminants;

“contaminants” means particles (including dusts, mists, and fumes)and/or other substances that generally may not be considered to beparticles (e.g., organic vapors, et cetera) but which may be suspendedin the ambient air;

“crown space” means the space between a wearer's head and the interiorside of a helmet;

“downstream” means located at point in time in an air stream later thanthe reference point to which it refers;

“exhaled air” means air that is exhaled by a person;

“filtering device” means a device that is designed to removecontaminants from air;

“filter media” or “filter element” means an air permeable material thatis designed to remove contaminants from air that passes through it;

“fluid inlet” means an area, surface, or volume of space through whichair can enter;

“filter layer” means an air-permeable structure that includes one ormore layers and that is designed to remove contaminants from air thatpasses through it;

“fluid outlet” means an area or portion through which air can exit;

“HEPA class” and “High Efficiency Particulate Air class” define theperformance of filter material as set forth in 42 C.F.R. §84 (1995);

“helmet” means an apparatus that is adapted to be worn on the head of aperson for purposes of protecting the head from impact;

“housing” means a structure or combination of parts that is fashionedfor housing or containing another item, wholly or partially;

“interior gas space” means the space in front of a person's face whereclean air can be inhaled;

“longitudinal axis” means an axis that extends generally along thelength of the filtering device;

“manifold” means a two or more channels or passageways that distributeair to or from a plenum;

“plenum” means a common volume of space where air flows into from morethan one location or from where air flows to more than one location;

“powered air purifying respirator” or “PAPR” means a device that iscapable of supplying clean air to a wearer where the air is filtered onthe wearer through use of energy from a source other than the wearer;

“substantially the same” means within 10% of another;

“transverse axis” means an axis that extends generally perpendicular tothe longitudinal axis; and

“upstream” means located at a point in time in an air stream before thereference point to which it refers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a prior art filter support 110 useful ina helmet-mounted respirator.

FIG. 2 is a perspective view of known device 200 for maintaining a knownfiltering bag in an arcuate shape.

FIG. 3 is a side view of the prior art filtering device 200 placedwithin the confines of a helmet 300.

FIG. 4 is perspective view of a filtering device 10 in accordance withthe present invention.

FIG. 5 is a perspective view of the filtering device 10′ having theupper half 14 of the housing 12 being removed.

FIG. 6 is a cross section of the filtering device 10′ taken along lines6-6 of FIG. 5.

FIG. 7 is a side view of the filtering device 10 positioned in a helmet70.

FIG. 8 is a perspective view of a filtering device 10′ having ports90-96 located thereon for measuring pressure in the various subsectionsof the filtering 10′.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the practice of the present invention, a filtering device is providedwhich includes a housing, an inlet, a first air distribution system, asecond air distribution system, and an outlet. The housing includes aplurality of subsections where each subsection is adapted to receive atleast one filter element. The inlet is disposed at a first location onthe housing. The first air distribution system is in fluid communicationwith the inlet and with each of the subsections. The second airdistribution system is located in fluid communication with eachsubsection. The outlet is in fluid communication with the second airdistribution system. The first and/or second air distribution systems isor are constructed to cause substantially the same airflow velocitythrough each subsection. This may be accomplished by designing theplenum(s), manifold(s), and/or ports (leading into and out of thesubsections) that comprise the air distribution system(s) to achievesuch substantially similar airflow velocity. If the pressure drop in thesubsection is too low, for example, the channels or passageways leadingto such subsection may be enlarged, in conjunction with an enlarging ofthe cross section of the port leading into or out of the subsection. Ifthe pressure drop is too high, the converse may be carried out to lowerthe pressure drop so that substantially the same airflow velocity isachieved.

FIG. 4 shows a filtering device such as a filter cartridge 10 that canbe used in a personal respiratory protection device to provide the userwith clean air to breathe. The filtering device 10 includes a housing 12that has an upper portion or half 14 and a lower portion of half 16. Airthat is to be filtered enters the housing 12 at an inlet 18 and exitsthe device at an outlet 20. The air thus passes through the device inthe direction of the arrow 22. The air that enters the device 10 atinlet 18 is unfiltered, whereas air that exits the device at outlet 20is filtered—that is, it is clean air safe for a user of the device tobreathe. As the air moves through the housing interior, the air passesthrough one or more filter elements where contaminants can be removedfrom the airstream. The housing 12 may be curved in the longitudinaldimension as shown, that is, around the transverse axis, so that thedevice may be used as a cartridge located in the crown space of ahelmet. The housing 12 also could be curved perpendicular to thelongitudinal dimension or along the longitudinal axis or dimension tofurther accommodate the crown space in a helmet. The first and secondportions 14 and 16 of the housing 12 are joined together at a midline24. The device may be separated along line 24 to replace the filterelements if so desired.

FIGS. 5-6 show the filtering device in a planar rather than a curvedconfiguration. In these figures, the top portion 14 (FIG. 4) of thehousing 12 is removed so that the housing interior may be seen, as wellas the filter elements 26, 28, and 30 located in subsections 32, 34, and36, respectively. The subsections 32, 34, and 36 provide a defined areafor the filter elements 26, 28, and 30 to reside within the housing 12.The subsections 32, 34, and 36 are not in fluid communication with eachother. In addition to the housing 12, the filtering device 10′ includesan inlet 18, a first plenum 38, a second plenum 40, and an outlet 20.The first plenum 38 is in fluid communication with the inlet 18 and witheach of the subsections 32, 34, and 36. The second plenum 40 also islocated in fluid communication with each subsection 32, 34, and 36. Theoutlet 20 also is in fluid communication with the second plenums 40. Thefirst and second plenum 38, 40 and the air manifolds that are associatedwith them are constructed to cause the same airflow velocity througheach subsection 32, 34, and 36. Air that enters the first plenum 38 fromthe inlet 18 passes in one of three different directions toward one ofthe three subsections 32, 34, and 36. Air may travel to the firstsubsection 32 through the opening or port 41 in the subsection 32 at thefirst end 42. The opening in the subsection 32 is defined at the firstend 42 by subsection sidewalls 44 and 46 and the top half 14 (FIG. 4) ofthe housing 12. Ambient air passing to the second and third filterelements 28 and 30 may do so through upper channels 48 and 50,respectively, as noted by air flow lines 51 and 53. Air that passesthrough the opening 41 at the first end 42 of first subsection 32 passesthrough the face 56 of the first filter element 26; air that passesthrough the opening 54 of the second subsection 34 passes through theface 58 of the second filter element 28; and air that passes through theopening 59 of the third subsection 36 passes through the face 60 of thethird filter element 30. Air exiting the second and third subsectionsafter being filtered passes through passageway 52 and opening 61,respectively, to enter plenum 40.

FIG. 6 shows, in particular, that each subsection may include first andsecond filter elements. Illustrated middle subsection 34, for example,includes opposing filter elements 28 and 62. Air arrives at filterelement 62, through lower channel 64, in a manner similar to airarriving at filter element 28 through upper channel 48 as describedabove. Each filter element 28 and 62 is tilted relative to the airentering the subsection to enable the air to better pass through thefilter media. Air that passes through filter elements 28 and 62 entersplenum 64 to then pass into passageway 52 where it then is directed outexit port 66 (FIG. 5) to enter plenum 40. Air in subsection 32 (FIG. 5)similarly passes through opposing filter elements to enter a centralplenum where it then is subsequently directed into passageway 68. Splitflow of the airstream may be carried out as described in U.S. patentapplication entitled Split Flow Filtering Device (U.S. Ser. No.13/310,881) to Billingsley et al. Although the filtering device of thepresent invention is shown with three subsections, the device may beconstructed to have 2, 3, 4, 5 to 10, 20 or more subsections. Theairflow velocity through each subsection is substantially the same,preferably within about 5% of each other.

FIG. 7 shows an example of a curved filtering device 10 in accordancewith the present invention being used in the crown space of a helmet 70of a PAPR 72. Clean air 74 that exits the filtering device 10 enters theinterior gas space 76 of the helmet 70 where it can be inhaled by thewearer. Atmospheric air is supplied to the fluid inlet 18 of the device10 via a conduit 78. A blower 80 drives or forces the unfiltered air 82through the conduit 78 into the inventive filtering device 10. Theblower 80 can be operatively powered by a suitable power source such asa battery, which may exhibit passivation—see U.S. Pat. No. 7,947,109 toSayers et al. The blower 80 can be positioned on a belt worn by thewearer. It also can be isolated from the exterior environment—see U.S.Pat. No. 6,796,304 to Odell et al.; see also U.S. Pat. No. 6,823,867 toAvery et al. The air flow also can be calibrated in the respiratorsystem—see U.S. Pat. No. 6,666,209 to Bennett et al. and managedotherwise—see U.S. Pat. No. 7,197,774 to Curran et al. A flow indicatormay be used to alert the wearer if air flow falls below a predeterminedvalue. Because air passes through a plurality of subsections, moresurface area is available for filtering, thereby lowering the pressuredrop across the device 10. Lower pressure drop means that less energy isneeded to drive the ambient air through the filter media. Further theadditional surface area may extend the service life of the media sinceit may take longer for the pores in the media to become plugged withvarious contaminants. The helmet could be, for example, a weldinghelmet—see, for example, U.S. Pat. No. 6,934,967 to Miyashita et al. andU.S. Pat. No. 7,637,622 to Magnusson et al.—with a head suspensionsystem (U.S. Pat. No. 6,367,085 to Berg. The invention also could beused in a hooded device—see U.S. Pat. No. 7,104,264 to Lee et al.

The plenums and manifolds of the air distribution systems may be definedby the shape and configuration of the housing and the first, second,third, and other subsections. The plenum may include physical structurethat assists in providing structure to the overall device and themanifolds may include the physical structure that is used to define thechannels and passageways that assist in splitting fluid flow into two ormore flow streams towards two or more independently operating filtermedia containing subsections.

The housing may be fashioned from a variety of materials into a variousshapes. Examples of materials from which the housing may be made includeplastics, metals, pressed or bonded fibrous composite structures.Depending on the materials used, and the desired structure of theresulting device, the housing may be made by various techniques,including injection molding, vacuum forming, die cutting, rapidprototyping, three dimensional computer aided manufacturing, stamping,die extrusion, and casting. The housing also could be a roll-basedproduct—see for example, U.S. patent application Ser. No. 12/784,182 toBillingsley et al. The housing and the construction of the subsectionsmay define the location of the filter layers relative to one another andto the overall structure.

The filter elements that are used in connection with the presentinvention may include one or more layers of particulate and/or gaseousfilter media. Particulate filter media is fashioned to removeparticulates that are suspended in the ambient air, and the gaseousmedia is fashioned to remove vapors that are suspended therein. Thefiltration layers may come in a variety of shapes and forms and forrespirator use may have a thickness of about 0.2 millimeters (mm) to 2centimeter (cm), or 0.5 to 1.5 cm, and it could be a generally planarfilter or it could be corrugated to provide an expanded surfacearea—see, for example, U.S. Pat. Nos. 5,804,295 and 5,656,368 to Braunet al. Each filtration layer also may include multiple filtration layersjoined together by an adhesive or any other means. The filter layersalso may include parallel channels as described, for example, in U.S.Pat. Nos. 6,752,889 and 6,280,824 to Insley et al. The filter media alsomay be a HEPA class filter. Essentially any suitable material that isknown (or later developed) for forming a filtering layer may be used forthe filtering material. Webs of melt-blown fibers, such as those taughtin Wente, Van A., Superfine Thermoplastic Fibers, 48 Indus. Engn. Chem.,1342 et seq. (1956), especially when in a persistent electricallycharged (electret) form are especially useful (see, for example, U.S.Pat. No. 4,215,682 to Kubik et al.). These melt-blown fibers may bemicrofibers that have an effective fiber diameter less than about 20micrometers (μm) (referred to as BMF for “blown microfiber”). Effectivefiber diameter may be determined according to Davies, C. N., TheSeparation Of Airborne Dust Particles, Institution Of MechanicalEngineers, London, Proceedings 1B, 1952. BMF webs that contain fibersformed from polypropylene, poly(4-methyl-1-pentene), and combinationsthereof are commonly used. Electrically charged fibrillated-film fibersas taught in van Turnhout, U.S. Pat. Re. 31,285, also may be suitable,as well as rosin-wool fibrous webs and webs of glass fibers orsolution-blown, or electrostatically sprayed fibers, especially inmicrofilm form. Electric charge can be imparted to the fibers bycontacting the fibers with water as disclosed in U.S. Pat. No. 6,824,718to Eitzman et al., U.S. Pat. No. 6,783,574 to Angadjivand et al., U.S.Pat. No. 6,743,464 to Insley et al., U.S. Pat. No. 6,454,986 and U.S.Pat. No. 6,406,657 to Eitzman et al., and U.S. Pat. No. 6,375,886 andU.S. Pat. No. 5,496,507 to Angadjivand et al. Electric charge also maybe imparted to the fibers by corona charging as disclosed in U.S. Pat.No. 4,588,537 to Klasse et al. or by tribocharging as disclosed in U.S.Pat. No. 4,798,850 to Brown. Also, additives can be included in thefibers to enhance the filtration performance of webs produced throughthe hydro-charging process (see U.S. Pat. No. 5,908,598 to Rousseau etal.). Fluorine atoms, in particular, can be disposed at the surface ofthe fibers in the filter layer to improve filtration performance in anoily mist environment—see U.S. Pat. Nos. 6,398,847 B1, 6,397,458 B1, and6,409,806 B1 to Jones et al. Typical basis weights for electret BMFfiltration layers are about 10 to 100 grams per square meter. Packedbeds of active-particulate also may be used as well as permeable shapedstructures of active-particulate which are held together with, forexample, PSA microparticulate—see U.S. Pat. No. 6,391,429 to Senkus etal.—or bonded sorbent particulate as described in U.S. Pat. No.5,033,465 to Braun et al. An example of a fibrous matrix that containsactive particulate is shown in U.S. Patent Application No.2005/0169820A1. The sorbent particles may be enmeshed in the web,typically, such that there is at least about 60 weight percent sorbentparticles enmeshed in the web. The fibers used in theparticle-containing web typically have sufficiently greatercrystallization shrinkage than similar fibers. The fibers typicallycomprise polypropylene, and the sorbent particles are typically evenlydistributed in the web so that the web has an Adsorption Factor A of atleast 1.6×10⁴/millimeters (mm) water. The porous sheet articlestypically exhibit a low pressure drop, have a long service life, andhave an Adsorption Factor A exceeding that of packed-bed carbon. TheAdsorption Factor A can be calculated using parameters or measurementssimilar to those described in Wood, JOURNAL OF THE AMERICAN INDUSTRIALHYGIENE ASSOCIATION, 55(1):11-15 (1994). Further information regardingAdsorption Factor A may be found in the U.S. patent application citedabove in this paragraph. The active-particulate that may be used in thefilters of the present invention include particles or granules that aresuited to perform some action or function attributable to somecharacteristic or property, including chemical change properties such asreaction, catalysis, and ion exchange, and/or physical properties suchas high surface area, porosity, and relatively small size and shape. Oneexample of active-particulate is particles that interact with componentsin a fluid to remove or alter their composition. The components in thefluid may be sorbed onto or into the active-particulate, or they may bereacted to make their composition more benign. The active-particulateaccordingly may be sorptive, catalytic, or reactive. Examples ofactive-particulate materials that may be used in connection with thepresent invention include sorbent microparticulate granules, such asactive carbon, chemically surface-treated activated carbon, alumina,silica gel, bentonite, kaolin diatomaceous earth, powdered zeolites(both natural and synthetic), ion exchange resins and molecular sieves,and particulates such as catalytic particles and particles containingencapsulated compounds. Commonplace active-particulates includeactivated carbon, chemically-treated carbon, and alumina particulate.Examples of commercially available activated carbon that may be used inthe present invention include Kuraray 12×20 type GG (available fromKuraray Chemical Corporation, Osaka, Japan and Calgon 12×30 URCavailable from Calgon Carbon Corporation, Pittsburgh, Pa. Patents thatdescribe various types of active-particulate that may be used in thepresent invention include U.S. Pat. No. 7,309,513 to Brey et al., U.S.Pat. No. 7,004,990 and U.S. Pat. No. 6,391,429 to Senkus et al., U.S.Pat. No. 6,767,860 to Hem et al., U.S. Pat. No. 5,763,078 to Braun etal., and U.S. Pat. No. 5,496,785 to Abler.

Although the invention has been described and illustrated for use inconjunction with personal respiratory protection devices like weldinghelmets and PAPRs, the invention also could be used with collectiveprotection system or installations like buildings and tents. In suchinstances a plurality of tuned filtering devices—or stacks of suchdevices—could be used to filter air before it enters the building orinstallation; see, for example, U.S. Pat. No. 7,995,570 to Insley et al.

EXAMPLE

Air Flow Test

To verify that the air flow velocities through the subsections of afilter are substantially equal, differential air pressure between thefilter subsections and ambient air pressure is measured. If ambient airpressure is not used, the baseline or reference pressure must measurethe air velocity of all of the filter air flow and not a subset of thesubsections. The pressure measurements can be done without filter mediain the subsections or with the filter media in the subsections. If thefilter media is located in the subsections during the measurements, thefilter media used must be essentially the same in each of thesubsections pertinent to the invention. The pressure measurement portsfor the subsections that are not being measured must be plugged. Thedifference between the baseline value and each subsection is recorded.

Air Filter Construction

A filter housing was designed and built, which contained six filterelements that were located in three subsections similar to the filteringdevice shown and described with reference to FIGS. 5-6. The airdistribution systems for each of three subsections were designed so thateach subsection would have equal air flow leading to it and away fromit. Pressure measurement ports 90, 92, and 94 were located in each ofthe three subsections, respectively, as well as at a port 96 located atthe outlet plenum of the filter as shown in FIG. 8. Port 96 measured thebaseline pressure. The filter elements used in each subsection containedparticulate filtering media and carbon loaded web to filter gaseouscontaminants. The filter media used is described in U.S. PatentApplication 2005/0169820 A1 to Tatarchuk et al. This filter mediaexhibited a measureable air flow resistance and contained activeparticulate entrapped within a matrix of microfibers.

Twenty-five liters per minutes of air were passed through the filterhousing 12. An Extech 755 handheld device was used to measure thepressure difference between the outlet 96 and each of the subsections90-94 according to the Air Flow Test. The pressure measurements betweenthe three sections are set forth below in Table 1:

TABLE 1 Ports Pressure Difference Volume Flow Measured (Pa) (lpm) 90 and96 4.8 25 92 and 96 4.8 25 94 and 96 4.8 25

The data in Table 1 show that the pressure measured in each filteringsubsection is similar the other subsections. The relative airflowvelocity through each of the three subsections in the filtering devicetherefore is substantially the same. Having similar airflow velocities,the filtering device would be expected to exhibit benefits of extendedservice.

This invention may take on various modifications and alterations withoutdeparting from its spirit and scope. Accordingly, this invention is notlimited to the above-described but is to be controlled by thelimitations set forth in the following claims and any equivalentsthereof.

This invention also may be suitably practiced in the absence of anyelement not specifically disclosed herein.

All patents and patent applications cited above, including those in theBackground section, are incorporated by reference into this document intotal. To the extent there is a conflict or discrepancy between thedisclosure in such incorporated document and the above specification,the above specification will control.

What is claimed is:
 1. A powered air purifying respirator (PAPR) airfiltering device that comprises: (a) a housing that includes a pluralityof subsections, each subsection constructed for receiving a filterelement; (b) an inlet disposed at a first location on the housing; (c)an upstream air distribution system in fluid communication with theinlet and with each of the subsections; (d) a downstream airdistribution system located in fluid communication with each subsection;and e) an outlet in fluid communication with the downstream airdistribution system; wherein the upstream and/or downstream airdistribution systems are constructed to cause substantially the sameairflow velocity through each subsection, and wherein the housing iscurved along a longitudinal axis such that the housing is configured tobe located within a crown space of a helmet.
 2. The filtering device ofclaim 1, wherein the device is a filter cartridge that is adapted foruse in a personal respiratory protection device.
 3. A personalrespiratory protection device that contains the filter cartridge ofclaim
 2. 4. The filtering device of claim 1 wherein the housing has anupper portion and a lower portion, and wherein air that is to befiltered enters the housing at the inlet and exits the device at theoutlet such that the air that enters the device at inlet is unfiltered,whereas the air that exits the device at outlet is clean air, andwherein the air that moves through the housing passes through one ormore filter elements where contaminants can be removed from theairstream.
 5. The filtering device of claim 1, wherein the upstream anddownstream air distribution systems each contain a plenum and amanifold.
 6. The filtering device of claim 5, wherein the filteringdevice contains 3 to 10 subsections within the housing.
 7. The filteringdevice of claim 6, wherein the plenums and manifolds cause the sameairflow velocity through each subsection.
 8. The filtering device ofclaim 1, wherein the air is delivered to each subsection through aplenum and one or more channels or passageways.
 9. The filtering deviceof claim 8, wherein the air leaving each subsection travels through oneor more channels or passageways.
 10. The filtering device of claim 1,wherein the air entering a subsection is split into two airstreams. 11.The filtering device of claim 10, wherein the split airstreams passthrough opposing filter elements before exiting the subsection.
 12. Thefiltering device of claim 1, wherein the airflow velocity in eachsubsection is within 5% of other subsections from a baseline value. 13.A powered air purifying device (PAPR) that contains the filtering deviceof claim
 1. 14. The powered air purifying device of claim 13, whereinthe PAPR includes a helmet, the device of claim 13 being disposed withinthe helmet.
 15. The powered air purifying device of claim 14, whereinthe PAPR includes a blower that supplies air to the inlet of thefiltering device.
 16. The powered air purifying device of claim 14,wherein the subsections each contain particulate and/or gaseous filters.17. The filtering device of claim 1, wherein each subsection contains aparticulate filter element that contains microfibers, and wherein eachsubsection contains a gaseous filter element that contains activeparticulate.
 18. The filtering device of claim 1, wherein eachsubsection contains a filtering element, and wherein each filter elementis tilted relative to the air entering the subsection.